This invention relates generally to blast furnaces, and relates specifically to an apparatus for equalizing pressure exerted on a device for feeding charge into a blast furnace.
A blast furnace is a tall shaft furnace which includes a cylindrical bottom portion, from which rises an upwardly-widening conically tapered bosh portion, surmounted by a taller tapered shaft structure which narrows towards the top, where it is closed by means of a top closing device which may include a small bell movably mounted in a small bell hopper, a large bell movably mounted in a large bell hopper, and an operating mechanism connected to the small bell and large bell for controlling the movement thereof. Such a furnace is operable to produce pig iron from charge fed stepwise through the top closing device. During such operation thereof, a gas known as "top gas" which includes carbon monoxide pollutants therein is formed in the blast furnace. Such top gas exerts full furnace pressure on the bottom surface of the large bell in the top closing device, which pressure is counterbalanced by the weight of the charge and the force exerted through the operating mechanism on the top surface of the large bell.
Presently, blast furnaces are operated at higher internal pressures so as to generate denser mixtures of gases which provide closer contact between the ore and the gases and generate increased production of pig iron. However, such higher internal pressures generate higher top gas pressures, which are not equalized by the weight of the charge and the force exerted through the operating mechanism, and therefor interfere with and prevent opening of the large bell for charging of the blast furnace.
Devices presently used to equalize the increased top gas pressure exerted on the bottom surface of the large bell direct gas from a remote location in the blast furnace system into the large bell hopper via lengthy ducts connected to scrubbers remotely located in the blast furnace system which remove pollutants from furnace gas enabling venting thereof to atmosphere. However, such presently used devices generate substantial pressure drops in the scrubbers and through the lengthy ducts connecting the remotely located scrubbers with the large bell hopper, which prevents equalization of such increased top gas pressure. Furthermore, such lengthy ducts connecting the remotely located scrubbers with the large bell hopper required extensive support systems for support thereof at substantial elevations above ground level, which exposed such ducts to ambient weather conditions, whereby during winter condensation in such ducts would freeze, interfering with operation thereof.
Such presently used devices further included a valve located at the interface of the large bell hopper and the ducts connecting the remotely located scrubber therewith. Such valve controls the flow of scrubbed gas into the large bell hopper. However, if such valve did not close completely, by virtue of sticking or inefficient operation thereof, upon opening of the large valve during the feeding of charge therethrough into the blast furnace, there was a back flow of polluted furnace gas into the scrubbed gas in the ducts leading into the large bell hopper, which pollutants were vented to atmosphere during opening of the small bell for feeding charge therethrough into the large bell hopper, thereby polluting the atmosphere. Furthermore, the frequent opening and closing of such valve during equalizing operation generated pockets of stagnent gas fromed in the lengthly ducts leading into the large bell hopper.
Such presently used devices included a further valve connected to the duct leading from the scrubbers to the large bell hopper, operable in the event of an explosion or slip in the blast furnace so as to vent scrubbed gas to atmosphere to relieve such pressure. However, as the lengthy ducts leading from the blast furnace to the scrubbers and from the scrubbers to the large bell hopper were remotely located from the blast furnace, such valve was inefficient in responding in a timely and adequate manner to such pressure surges.